The present invention relates to an abrasive-band grinding device for rolls, in particular crowned rolls, and a method for controlling an abrasive-band grinding device during the grinding of the faces of a roll, in particular crowned rolls.
The grinding of crowned rolls for paper machines is a particularly difficult and demanding process. For example, the diameter of large so-called Yankee cylinders can be up to 5 meters, in which case, correcting or finishing grinding of the crowned shape requires particular operations in order that a satisfactory surface quality may be achieved.
In the prior art, the use of an abrasive-band grinding device in the grinding of the faces of crowned rolls is known. In abrasive-band grinding devices, the band is driven from the output of a motor by means of a drive pulley. The band is arranged to run over two reversing pulleys, and a separate backup pulley, i.e., a so-called contact pulley, is arranged between the reversing pulleys. The contact pulley forms a back stop whereby the abrasive band is pressed at the backup pulley against the face to be ground. The use of an abrasive band is highly advantageous especially in large-scale grinding work, as compared, for example, with the use of a grindstone. The reason for this is because the wear of the grindstone must be monitored constantly in view of the fact that along with the wear of the stone, the control parameters and the geometry of the device are also changed. By contrast, this does not occur in the case of a band because the band can always be kept in contact with the crowned face to be ground. Also, by means of a band, it is possible to grind without a grinding fluid, whereas a stone operates best when a grinding fluid is used.
In a first conventional prior art grinding process, the grinding device is passed in a direction parallel to the axis of the crowned roll, and guide rails of the grinding device are also placed in a direction parallel to the axis of the crowned roll. The band or the grinding means is fed, in a typical construction, in a direction perpendicular to the axial direction of the roll. The device is transferred after each grinding cycle further in the axial direction of the roll to be ground. In such a case, the grinding result becomes serrated.
It has been possible to avoid a serrated grinding result by means of a second prior art construction in which the grinding device has been arranged to follow a certain pattern. In this construction, the guides have been shaped curved in compliance with the crown form of the roll. A drawback of this type of device is the long time required when changing the settings of the device.
It is an object of the present invention to provide a novel solution for increasing the precision of grinding of faces of rolls in particular, crowned rolls.
It is another object of the present invention to provide new and improved grinding devices and methods in which separate guides are not needed, but rather, positive control of the backup or contact pulley is used.
In order to attain these objects, and others, in a grinding device in accordance with the invention, a backup pulley is inclined by means of a motor device along with the progress of grinding. Also, the contact pulley is always shifted so that the radius of the contact pulley at the grinding point always passes through the geometric axis of rotation of the crowned roll.
More specifically, the abrasive-band grinding device for rolls in accordance with the invention includes a looped abrasive band, rotation means coupled to the abrasive band for rotating the abrasive band, guide pulleys arranged in the loop of the abrasive band, a contact pulley arranged in the loop of the abrasive band between the guide pulleys and which presses the abrasive band against a face of the roll, and inclining means connected to the contact pulley for adjustably inclining the axis of rotation of the contact pulley. By inclining the axis of rotation of the contact pulley, the axis of rotation of the contact pulley may be maintained substantially parallel to the face of the roll and thus the abrasive band is pressed by the contact pulley in compliance with the face of the roll, i.e., it follows the contour of the face of the roll being ground. The inclining means may comprise an actuator or motor coupled directly or indirectly to the contact pulley, in which case, the device may include control means for controlling actuation of the actuator and thus the inclination of the axis of rotation of the contact pulley.
In certain embodiments, the grinding device includes a first stationary frame, a second frame arranged on the first frame and movable with respect thereto, and a third frame arranged on the second frame and movable with respect thereto. First bearing means are provided for revolvingly mounting the contact pulley on the third frame, and second bearing means are provided for pivotally mounting the third frame on the second frame. If the inclining means comprise a motor, it is preferably mounted at one end on the second frame and coupled at the other end to the third frame. The first bearing means may comprise a pair of bearings arranged on the third frame, one at each transverse side of the contact pulley, and the second bearing means may comprise a pair of bearings arranged on the second frame, one on each radial side of the contact pulley.
In addition to a motor, the inclining means may comprise control means connected to the motor for controlling the motor, and a spindle coupled to the motor and to the third frame. The motor displaces the spindle along a linear path, or if the spindle is a ball-screw device, simply displaces the same.
In the method in accordance with the present invention, both the inclination of the contact pulley and the position of this pulley in relation to the roll face are regulated. Both regulations are carried out under microprocessor control by means of separate motors, preferably electric stepping motors. It is possible to program the desired crown form of the face to be crowned in the microprocessor in advance of the actual grinding process.
More specifically, in certain embodiments, in the method for grinding rolls in accordance with the invention, a looped abrasive band is guided over guide pulleys, a contact pulley arranged in the loop of the abrasive band is pressed toward the roll to be ground such that the abrasive band is pressed thereby against a face of the roll to be ground, and the axis of rotation of the contact pulley is adjustably inclined in order to maintain the axis of rotation of the contact pulley substantially parallel to the face of the roll such that the abrasive band is pressed by the contact pulley in compliance with the face of the roll. In other words, the contact pulley may be inclined until the face of the contact pulley is substantially parallel to a tangent of the roll at each grinding point.